Now you see my knots now you don't on my Cobra 4

[veritasleather]

Hey guys!

Im a noob here, first post. I recently acquired a Cobra 4 from the leather machine co. picked up from Dave about a month ago. Now my problem is that when I sew my knots pop up on top for about 4-5 stitches then they disappear for another 4-5 then they reappear. Please understand I am just learning how to drive this thing. Never used one before. is it me pushing or pulling the leather? or is this a tension problem? thank you guys!

Frank

[Wizcrafts]

It is either caused by an out of round or badly wound bobbin, or twisty/excessively bonded top thread, or rawhide in portions of the leather.

[OLDNSLOW]

Wiz, would you mind extrapolating on that just a bit more.  If winding the bobbin on the machine how can it be done incorrectly, assuming the bobbins being new is there a way to ensure they are all good, and what to look for in the thread.

thanks

O n S

Ron

[Wizcrafts]

If while winding a bobbin you have the little movable thread aiming guide misaligned on the left-top of the machine, the windings will build up on one side or the other (it should be adjusted to feed evenly across the bobbin, with good thread tension). Or, the bobbin loading thread may be jumping in and out of the bobbin winder's tension disks on top of the machine. A bobbin loaded thusly is unbalanced and may wobble as it feeds the thread through the tension spring. Or, if the owner leaves too much length on the starting thread stub, it may catch intermittently on the ejector/anti-backlash spring inside the bobbin case. This will cause the bobbin to feed in a jerky fashion, rather than smoothly. Finally, the bobbin itself may have been formed less than perfectly aligned on the disk ends. Or, the length of the bobbin may be under or over optimum length. I have accumulated 441 bobbins that have different lengths from end to end. The oversize bobbins tend to bind a bit in the shuttle and add unwanted tension to the bobbin thread, compared to a slightly shorter bobbin.

[OLDNSLOW]

Thanks for your input, so I guess it wouldn't hurt to put a caliper on a few bobbins to see if they are within spec.

[LumpenDoodle2]

Wiz is spot on as usual, especially regarding the quality of the bobbin.   You would be surprised how 'out of true' a new bobbin can be, and it will affect you machines stitch performance.   That, and winding you bobbins too loosely.

[veritasleather]

Thank you Wizcrafts, I am still using the bobbin that was loaded with the machine when I picked it up from the leather machine co. I think I will attempt to wind a bobbin myself per your comments. I hope this fixes things, again, am still learning. Trying to follow what all the leather machine co. videos suggest. The long leads of thread before starting to stitch also makes sense. I do notice the knots up first at the beginning of stitching then they might go back down for a couple of more stitches. Thanks guys!

[Darren Brosowski]

Could also be as simple as the thread not coming off the top spool evenly

 

[veritasleather]

 

Could also be as simple as the thread not coming off the top spool evenly

 

Thanks Darren, so what you mean is that it could also be that there is a problem with the top spool itself? Or tension is causing the un even feed?

[MADMAX22]

I believe he is talking about the spool of thread. If it doesn't come off smoothly it will mess with your top tension. Take your spool and gently pull thread off of it noting if there are any spots with a slight tension change like say it catches at one spot. This will translate to your stitches having momentary spots of very high top tension. I had a spool that was junking up on the bottom, top of the spool fed fine but bottom would stick and it would reak havic with my machine.

[mikesc]

Another thing that can give you intermittent ( but regular ) changes in the top tension, is dirt in the tension assembly , actually inside the barrel part that the "take up spring" sits into..any speck of dirt there will prevent the spring from compressing properly when it moves ( it should move smoothly in it's "slot"on the side of the tension assembly, no jerkiness at all ) and so the tension every few stitches will not be the same..this is even more evident on a "zig zag" machine, when it happens there the "knots" will be "above" on one end of the stitch, and below or correctly seated on the other..
Had this problem on a singer 20U33 that I picked up a week ago, fixed the problem yesterday when doing an "overall service", ordered new tension assembly ( along with some other stuff ) from College sewing yesterday.

re thread spools..if they sit uncovered for a while they get dusty*, the dust can be a little sticky, this will make them unwind with uneven tension, likewise if they have been dropped or stored with pressure on any part of them, always store them upright ( not squashed together ) and covered up from dust and other pollutants..

* To avoid this dust etc, stick a lightweight clear plastic bag with a hole in it at the top over each "cone", feed the thread out to the "eye" in the thread stand , and on down through the "thread path" through this hole..make sure it does not "snag" ..

Edited August 26, 2016 by mikesc

[veritasleather]

On August 25, 2016 at 10:40 PM, MADMAX22 said:

I believe he is talking about the spool of thread. If it doesn't come off smoothly it will mess with your top tension. Take your spool and gently pull thread off of it noting if there are any spots with a slight tension change like say it catches at one spot. This will translate to your stitches having momentary spots of very high top tension. I had a spool that was junking up on the bottom, top of the spool fed fine but bottom would stick and it would reak havic with my machine.

 

On August 26, 2016 at 2:30 AM, mikesc said:

Another thing that can give you intermittent ( but regular ) changes in the top tension, is dirt in the tension assembly , actually inside the barrel part that the "take up spring" sits into..any speck of dirt there will prevent the spring from compressing properly when it moves ( it should move smoothly in it's "slot"on the side of the tension assembly, no jerkiness at all ) and so the tension every few stitches will not be the same..this is even more evident on a "zig zag" machine, when it happens there the "knots" will be "above" on one end of the stitch, and below or correctly seated on the other..
Had this problem on a singer 20U33 that I picked up a week ago, fixed the problem yesterday when doing an "overall service", ordered new tension assembly ( along with some other stuff ) from College sewing yesterday.

re thread spools..if they sit uncovered for a while they get dusty*, the dust can be a little sticky, this will make them unwind with uneven tension, likewise if they have been dropped or stored with pressure on any part of them, always store them upright ( not squashed together ) and covered up from dust and other pollutants..

* To avoid this dust etc, stick a lightweight clear plastic bag with a hole in it at the top over each "cone", feed the thread out to the "eye" in the thread stand , and on down through the "thread path" through this hole..make sure it does not "snag" ..

MADMAXX22, I noticed when looking at my spool of thread that I had it set on the stand that the Leather Machine co. recommends for the bobbin thread spool. I don't know if this matters? So, this would be the stand farthest from the thread path. I will definitely check my spool of thread and see if it sticks anywhere, or if it pulls. 

mikesc, I will definitely clean out the tension assembly areas and look for dust and dirt. This all makes a lot of sense now. My machine is definitely in an area that can accumulate much dust. I will definitely look for snags.

thanks guys!

[JMWendt]

I've noticed with these machines that I tend to screw up  the thread occasionally when I remove an item from the work space.  Then on the next round of sewing, the thread is wrong . . . usually the second tension disk where I accidentally get a loop of string in the spring around it, or I get it so the string is completely out of the disk.  In the first case, the tension on the top string is too high, and I see knots on top.  In the second case, tension is too low and I see knots on bottom.  

I have also seen spools of thread that just unwind poorly from the thread stand, and they tend to twist into themselves then bind going through the feeder holes.  This seems to happen on stiffer bonded threads, or anything I made the mistake of leaving in the sun for a month.  My machine is near a window.

I'd check the thread path first before focusing on mechanical issues.  But if the thread path looks good, then I'd monitor the thread behavior during sewing . . . just watch what is happening and see when it gets tension and starts showing knots.  Then and only then would I start to look for mechanical issues.

[veritasleather]

7 hours ago, JMWendt said:

I've noticed with these machines that I tend to screw up  the thread occasionally when I remove an item from the work space.  Then on the next round of sewing, the thread is wrong . . . usually the second tension disk where I accidentally get a loop of string in the spring around it, or I get it so the string is completely out of the disk.  In the first case, the tension on the top string is too high, and I see knots on top.  In the second case, tension is too low and I see knots on bottom.  

I have also seen spools of thread that just unwind poorly from the thread stand, and they tend to twist into themselves then bind going through the feeder holes.  This seems to happen on stiffer bonded threads, or anything I made the mistake of leaving in the sun for a month.  My machine is near a window.

I'd check the thread path first before focusing on mechanical issues.  But if the thread path looks good, then I'd monitor the thread behavior during sewing . . . just watch what is happening and see when it gets tension and starts showing knots.  Then and only then would I start to look for mechanical issues.

My machine is also in a hot spot, I will definitely check the behavior of the thread and go from there ,

thanks!

[brmax]

Sometimes the install of the bobbin can add tension if its installed to unload in a particular direction, and some operators may use this in a quick check way also.

I would be interested in any relationship discussion within this thread path : )

Floyd

[MADMAX22]

Speaking of bobbins, I have noticed I have some where both round end plates are the same thickness, others have thicker material on one end and thinner on the other. 

Anyone else notice this.